<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>设置断点</title>
</head>
<body>
<p id="demo"></p>
<p>开启调试工具，在代码执行到第三行前会停止执行。</p>
<script>
    var x = 15 * 5;
    debugger;
    document.getElementById("demo").innerHTML = x;
</script>
</body>
</html>